Ingnitor for internal combustion engines

ABSTRACT

An ignition device for internal-combustion engines, wherein a spark gap is, energized by a voltage pulse, has a transformer having primary and secondary windings, the secondary winding being connectable to the spark gap. An amplifier is connected to the primary winding and a magnetic circuit provides a magnetic field having an intensity which changes between determined values thereof. A galvanomagnetic sensing element is disposed in the magnetic field and is responsive to the changes in the field intensity. The sensing element is connected to the amplifier for controlling the flow of current through the primary winding so as to develop voltage pulses across the secondary winding for energizing the spark gap.

States Patent [72] inventors Siegmund Kreil Stockdorf; Erich Metzger,Munich, both of, Germany [21] Appl No 836,273 [22] Filed June 25,19691451 Patented June 15, 1971 [73] Assignee Siemens AktiengesellschaftBerlin, Germany [32] Priority July 4, 1968 [33} Germany [31] P17646149[54] INGNITOR FOR INTERNAL COMBUSTION ENGINES 7 Claims, 5 Drawing Figs.

[52] U.S. Cl 123/148E, 315/209 [51] Int. Cl F02p 3/02 [50] Field ofSearch 123/148, 148 E; 315/209 [56] References Cited UNITED STATESPATENTS 2,924,633 2/1960 Sichling et a1. 123/148 E Primary ExaminerLaurence M. Goodridge Attorneys-Curt M, Avery, Arthur E. Wilfond,Herbert L.

Lerner and Daniel J. Tick ABSTRACT: An ignition device forinternal-combustion engines, wherein a spark gap is, energized by avoltage pulse, has a transformer having primary and secondary windings,the secondary winding being connectable to the spark gap. An amplifieris connected to the primary winding and a magnetic circuit provides amagnetic field having an intensity which changes between determinedvalues thereof; A galvanomagnetic sensing element is disposed in themagnetic field and is responsive to the changes in the field intensity.The sensing element is connected to the amplifier for controlling theflow of current through the primary winding so as to develop voltagepulses across the secondary winding for energizing the spark gap.

INGNITOR FOR INTERNAL COMBUSTION ENGINES Our invention relates to anignitor for internal combustion engines wherein a spark gap is energizedby a voltage from the secondary of a transformer in 'which the primarywinding is excited in response to mechanically controlled short-intervalchanges.

A mastering of the ignition process is important for the efficientoperation of vehicles powered by internal-combustion engines. Presentday ignition systems almost all utilize mechanical means which mostoften comprise break contacts actuated by a cam shaft. Such means areunfortunately subjected to considerable wear.

The first attempts at reducing the vulnerability of ignitors areexemplified by the popularly termed transistor or thyristor ignitionswhich, in addition to increasing the ignition output relative to theabove devices, reduce the current load of the break contacts, andthereby reduce the wear caused by burnoff. However, reducing theintermittent current causes, at the same time, an increase in theunreliability of contact which can easily lead to undesired disturbancesespecially when the thyristor fires. In addition, the mechanical wearassociated with camshaft control is not at all reduced.

It is also known to use a photoelectric technique wherein a cylinderprovided with slits rotates between a light source and a photo cell andinitiates the firing process via an appropriate transistor circuit at areference value obtained from the photo element. Although thisarrangement reduces wear and renders the breaker mechanism superfluous,it too has proved very vulnerable to disturbances particularly when usedin a vehicle.

Accordingly, it is an object of our invention to provide a new andimproved ignitor which overcomes the aforementioned disadvantages of theknown techniques.

It is still another object of our invention to provide an ignitor inwhich no wear occurs between parts thereof moving relative to eachother. Subsidiary to this object it is an object of our invention toprovide an ignitor wherein the energization of the spark gap iscontrolled in dependence upon changes in the flux intensity of amagnetic field.

According to a feature of the invention, a galvanomagnetic resistor,which acts to electrically control the primary side of the transformer,for example via an amplifier, in response to the movement of a permanentmagnet relative to the galvanomagnetic resistor. A rotating magnetassembly is preferably used in achieving the objects of the invention.The galvanomagnetic resistance consists, preferably, of a so-calledfield plate as disclosed, for example, in US. Pat. Nos. 3,267,404 and3,260,980. Such field plates may be substituted by other types ofgalvanomagnetic resistance devices such as, for example, galvanomagneticPN diodes.

The field plate can be placed upon a carrier, for example, in the shapeof a narrow strip. It is preferable to use a stationary field platesince this makes contacting simpler and the two current leads easilyaccessible. The leads to the field plate are preferably laid over thecarrier. Typically, the cylindrical magnet carrier is seated on thedistributor shaft of the motor and is equipped along its periphery witha number of equally spaced control magnets, this number corresponding,for example, to the number of cylinders of the motor. The changes whichoccur in the field plate with respect to its resistance value R areplotted as a function of the magnitude of the angle of rotation of thedistributor shaft in the diagram according to FIG. 1.

The invention will now be elucidated with reference to the drawings inwhich:

FIG. I, as already mentioned, is a graph depicting the variation of theresistance of the field plate as a function of the angular movement ofthe distributor shaft.

FIG. 2 is a schematic representation, partially in section, of apreferred embodiment of the invention in which a permanent magnet iscoaxially mounted to a distributor shaft.

FIG. 3 is a plan view of the embodiment illustrated in FIG. 2.

FIG. 4 is a schematic diagram of an amplifier and trans former used totranslate the control signal initiated by the field plate to a voltagefor energizing the spark gap.

FIG. 5 is a schematic diagram of the amplifier preferred for use withthe embodiment of the invention according to FIG. 2.

Referring to FIGS. 2 and 3, a ring-shaped permanent magnet 1 is providedat its top and bottom surfaces with coaxially positioned annular plates2, 3 consisting of magnetic permeable material such as soft iron. Themagnet I and plates 2, 3 are mounted on shaft 4 so as to be coaxialtherewith, the shaft 4 being, for example, the distributor shaft of aninternal-combustion engine. The annular plates 2., 3 function as polesfor the magnet. The plates 2,3 are bridged at periodic intervals by asoft iron yoke 6 which is laterally arranged and contains a field plate5. This is achieved by providing one of the two rings 2, 3 for example,the upper ring 3, with equidistant radial projections 3' while the otherring 2 maintains a narrow distance from the bottom leg of the yoke 6,this distance being unchanged during the entire rotation. The profile ofthe bulges 3 is adjusted to the profile of the upper leg of the yoke 6and ends accordingly in a pointed tip as does the latter so that themagnetic flux across the yoke is closed only for short intervals of timeduring the travel of each projection 3 past the upper leg of the yoke 6.

The soft iron yoke 6 is subdivided into two parts, preferably throughits center. The disc-shaped field plate 5 comprised of semiconductormaterial is disposed between these two parts in such a manner that theentire magnetic flux which closes across the yoke also crosses the fieldplate 5. The electrical terminals of the field plate are indicated byreference numeral 7 and the stationary base plate which carries the yokeis indicated by reference numeral 8.

Although the foregoing discloses an embodiment wherein the permanentmagnet and its pole plates are mounted coaxially with the distributorshaft, it is also possible to mount a permanent magnet on the shaft sothat it is eccentric with respect to the shaft axis.

The diagram corresponds qualitatively to the characteristic which may beexpected in connection with the embodiment of FIGS. 2 and 3. The primaryadvantage of the above-described device is that it is simple to produceand affords high operational reliability, particularly with regard toimperviousness to contamination.

The changes which occur in the galvanomagnetic resistance memberaccording to FIG. I. during the operation of such a device or similardevices can be made to act upon the primary side of an ignitiontransformer in a number of ways. Especially preferred is the switchingarrangement illustrated in FIG. 4, which can be further developed to thearrangement shown in FIG. 5.

Referring first to FIG. 4, the spark gap 11 is energized by thesecondary winding of the ignition. transformer or ignition coil. Thebase of a switching transistor 13 lies at the center tap of a voltagedivider formed with fixed resistance 14 and the galvanomagneticresistance 15 which can correspond, for example, to the field plate 5 ofa device according to FIGS. 2 and 3. The fixed resistor 14 is in theemitter-base circuit and the field plate 15 is in the collector-basecircuit. The primary coil of the ignition transformer 12 is connected inseries with the fixed resistor 14 and with the emitter of the switchingtransistor 13. The elements 14 and 15 of the voltage divider aredimensioned so that the switching transistor 13 conducts when the fieldplate 15 is not passed by magnetic flux. The supply voltage which canbe, for example 6 volts direct voltage, is supplied as shown in FIGS. 4and 5.

When the magnetic flux acts upon the field plate 15, its resistancevalue rises. Transistor I3 turns off interrupting the current throughthe primary winding of the ignition transformer 12 and releases anignition voltage at the spark gap 11 in accordance to Lenz's law. In theinterest of optimum effectiveness, it is recommended that the followingconditions be established:

l. The keying ratio or duty cycle should be chosen so that even at highimpulse frequency, which corresponds to a high r.p.m. of the shaft, theoccurrence of the highest possible field strength in the field plate isassured, and

2. The leading edge of the control pulses must be sufficiently steep.

The requirement of condition (I) can be fulfilled with control magnetshaving an appropriately small width. Condition (2) is fulfilled by usingshaping circuits which are controlled by the transistor. In thisconnection, reference is made to the embodiment illustrated in FIG. 5which can be regarded as an optimum embodiment of the invention whentaken together with a device according to FIGS. 2 and 3.

In FIG. 5, the voltage divider l4, 15, which is connected together withthe transistor 13 is already discussed in connection with FIG. 4,delivers a suitable control voltage to a shaping circuit for increasingthe steepness of pulse edges with transistors 13 and 16. Resistance 14is again a fixed resistance, resistance 15 is galvanomagnetic sensingelement or member. The shaping circuit with the transistors 13 and 16has the characteristic of flipping from one stable state to another whenthe voltage at the base of the transistor 13 rises to a specificthreshold value. This is caused by the amplification which is determinedby resistances I7, 18 and 19 in coaction with the feedback via thecommon emitter resistance 20. The steeper voltage characteristic at thecollector of the transistor 13 controls, via resistor 18, a transistor21 whose saturation current is so high that it can switch a powertransistor 22 which is connected in series with the primary winding ofthe ignition transformer. Ignition firing occurs when the circuittriggers at the leading edge of the voltages at the base of transistor13 and transistor 22 suddenly interrupts the current through the primarywinding of the ignition transformer 12. The high, positive voltage whichoccurs at this moment at the emitter of the transistor 22 is limited bythe Zener diode 23 to a specific value in order to protect thetransistor 22. The bistable flip-flop circuit provided in a deviceaccording to FIG. 5 thus ensures the appearance of a voltage at thespark gap 11 which is virtually independent on the instantaneousmovement speed, more particularly on the rotary speed of the controllingpermanent magnet.

In this connection, attention is called to the fact that thegalvanomagnetic resistance of a device of the present invention can alsocontrol other bistable flip-flop circuits, particularly with suchcircuits built-up of semiconductor components. Bistable flip-flopsdeliver a voltage pulse at the triggering instant with requiredintensity in the secondary portion of the ignition transformer and soalso at the spark gap.

The advantages of a device according to the invention include affordingthe use of magnetically controlled field plate resistance several ofwhich can be used in a single device. The invention provides acontact-free ignition-voltage switch that meets the requirements for therugged operation of gasoline engines. The life span afforded by theinvention can be considered to be unlimited since mechanical wear andtear are virtually completely eliminated. Most of all, the disadvantagesassociated with the known devices in respect to the occurrence ofresonance, frequency unreliability and in respect to making contact areeliminated, the latter introducing a very critical time delay when theclosing angle is unfavorable.

To those skilled in the art it will be obvious upon a study of thisdisclosure that our invention permits of various modifications and maybe given embodiments other than particularly illustrated herein, withoutdeparting from the essential features of the invention and within thescope of the claims annexed hereto.

We claim:

1. An ignition device for an internal combustion engine having spark gapmeans and a shaft rotatable in synchronism with the rotation of theengine, comprising a transformer having a primary winding and having asecondary winding for connection to the spark gap means, a permanentmagnet attached to said shaft so as to be rotatable therewith, astationary magnetizable yoke structure disposed adjacent to said rotatabe magnet structure and having a field gap, said rotatable magnet andsaid yoke structure conjointly defining a magnetic circuit for providinga magnetic field having an intensity that changes between values thereofin synchronism with the rotation of said shaft and said engine, agalvanomagnetic resistor disposed in said gap and having a resistancechangeable in response to changes in said magnetic field, and anamplifier comprising a voltage divider, a switching transistor and apower transistor connected in cascade, said voltage divider consistingof two two-pole members, one pole of one member being joined to one poleof the other member so as to form a tap, one of said members being saidgalvanomagnetic resistor and the other of said members being a fixedresistance, said tap being connected to the base of said switchingtransistor, the other of said poles of said one member being connectedto the collector of said switching transistor and the other of saidpoles of said other member being connected to the emitter of saidswitching transistor to convert the collector current of said switchingtransistor changes to pulses in response to said changes in saidgalvanomagnetic resistor, said switching transistor and said powertransistor conjointly defining a shaping network for increasing thesteepness of the edges of said pulses, said power transistor beingconnected to said primary winding of said transformer, whereby saidpower transistor interrupts the current in said primary winding inresponse to said pulses.

2. An ignition device according to claim 1, comprising a driver stageconnected intermediate said power transistor and said shaping network.

3. An ignition device according to claim 1, comprising a Zener diodeconnected across the output of said power transistor for protecting thelatter.

4. In an ignition device according to claim 1, said shaping networkincluding a additional transistor connected to the output of saidswitching transistor so as to define a bistable flip-flop circuitconjointly with the latter, whereby said flipflop circuit switches toone state with the occurrence of the leading edges of said pulses andswitches to the other state with the occurrence of the trailing edges ofsaid pulses.

5. In an ignition device according to claim 1, comprising twosingle-pole plates mounted on said shaft so as to be concentrictherewith, said permanent magnet being annular and disposed so as to besandwiched intermediate said plates and coaxial with said shaft, saidyoke structure being disposed laterally of said permanent magnet andsaid pole plates, said yoke being in two parts arranged so as toaccommodate said galvanomagnetic resistor therebetween, said yoke andsaid pole plates with said permanent magnet forming a magnetic circuitthe magnetic flux of which passes through said galvanomagnetic resistor;at least one of said pole plates having a noncircular shape so as tocause said magnetic circuit to sequentially close and open as saidplates and said permanent magnet are rotated on said shaft whereby theflow of flux crossing said galvanomagnetic resistor is sequentiallyinterrupted.

6. In an ignition device according to claim 5, said one plate havingprojections at respective locations equally spaced about the peripherythereof, whereby said projections sequentially pass close to said yoketo sequentially close and open said magnetic circuit when said shaftrotates.

7. In an ignition device according to claim 5, said two parts of saidyoke each consisting of soft iron.

1. An ignition device for an internal combustion engine having spark gapmeans and a shaft rotatable in synchronism with the rotation of theengine, comprising a transformer having a primary winding and having asecondary winding for connection to the spark gap means, a permanentmagnet attached to said shaft so as to be rotatable therewith, astationary magnetizable yoke structure disposed adjacent to saidrotatable magnet structure and having a field gap, said rotatable magnetand said yoke structure conjointly defining a magnetic circuit forproviding a magnetic field having an intensity that changes betweenvalues thereof in synchronism with the rotation of said shaft and saidengine, a galvanomagnetic resistor disposed in said gap and having aresistance changeable in response to changes in said magnetic field, andan amplifier comprising a voltage divider, a switching transistor and apower transistor connected in cascade, said voltage divider consistingof two two-pole members, one pole of one member being joined to one poleof the other member so as to form a tap, one of said members being saidgalvanomagnetic resistor and the other of said members being a fixedresistance, said tap being connected to the base of said switchingtransistor, the other of said poles of said one member being connectedto the collector of said switching transistor and the other of saidpoles of said other member being connected to the emitter of saidswitching transistor to convert the collector current of said switchingtransistor changes to pulses in response to said changes in saidgalvanomagnetic resistor, said switching transistor and said powertransistor conjointly defining a shaping network for increasing thesteepness of the edges of said pulses, said power transistor beingconnected to said primary winding of said transformer, whereby saidpower transistor interrupts the current in said primary winding inresponse to said pulses.
 2. An ignition device according to claim 1,comprising a driver stage connected intermediate said power transistorand said shaping network.
 3. An ignition device according to claim 1,comprising a Zener diode connected across the output of said powertransistor for protecting the latter.
 4. In an ignition device accordingto claim 1, said shaping network including a additional transistorconnected to the output of said switchiNg transistor so as to define abistable flip-flop circuit conjointly with the latter, whereby saidflip-flop circuit switches to one state with the occurrence of theleading edges of said pulses and switches to the other state with theoccurrence of the trailing edges of said pulses.
 5. In an ignitiondevice according to claim 1, comprising two single-pole plates mountedon said shaft so as to be concentric therewith, said permanent magnetbeing annular and disposed so as to be sandwiched intermediate saidplates and coaxial with said shaft, said yoke structure being disposedlaterally of said permanent magnet and said pole plates, said yoke beingin two parts arranged so as to accommodate said galvanomagnetic resistortherebetween, said yoke and said pole plates with said permanent magnetforming a magnetic circuit the magnetic flux of which passes throughsaid galvanomagnetic resistor; at least one of said pole plates having anoncircular shape so as to cause said magnetic circuit to sequentiallyclose and open as said plates and said permanent magnet are rotated onsaid shaft whereby the flow of flux crossing said galvanomagneticresistor is sequentially interrupted.
 6. In an ignition device accordingto claim 5, said one plate having projections at respective locationsequally spaced about the periphery thereof, whereby said projectionssequentially pass close to said yoke to sequentially close and open saidmagnetic circuit when said shaft rotates.
 7. In an ignition deviceaccording to claim 5, said two parts of said yoke each consisting ofsoft iron.